The present invention relates to a process for producing a thermoplastic elastomer composition by melt kneading rubber and a thermoplastic resin with an extruder, and to a thermoplastic elastomer composition.
A thermoplastic elastomer composition has found wide use in various fields such as car parts, electric appliance parts and miscellaneous goods, because (i) no vulcanization process is needed, and (ii) a conventional molding machine for a thermoplastic resin is usable when molding the thermoplastic elastomer composition.
As the thermoplastic elastomer composition, an olefinic thermoplastic elastomer composition and a styrenic thermoplastic elastomer composition are known. As the former composition, there are generally known (i) a non-cross-linked composition obtained by melt kneading an olefin copolymer rubber and an olefin polymer resin, and (ii) a cross-linked composition obtained by melt kneading an olefin copolymer rubber and an olefin polymer resin in the presence of a cross-linking agent such as an organic peroxide to perform dynamic cross-linking. As the latter composition, there are known compositions such as (i) a composition comprising a styrene-butadiene block copolymer and an olefin polymer resin, (ii) a composition comprising a styrene-isoprene block copolymer and an olefin polymer resin, and (iii) a composition comprising a hydrogenation product of said block copolymer and an olefin polymer resin.
As a process for producing a non-cross-linked thermoplastic elastomer composition, there is known a process wherein rubber and a thermoplastic resin are kneaded with a closed-type kneading machine such as a Banbury mixer and a kneader. However, said production process is not an efficient one, because the production process uses a batchwise kneading machine of low productivity such as a Banbury mixer and a kneader.
As a process for producing a cross-linked thermoplastic elastomer composition, there is known a process wherein rubber and a thermoplastic resin are kneaded in advance with a closed-type kneading machine such as a Banbury mixer and kneader; the resulting kneaded product is successively granulated to obtain pellets; and then the pellets and a cross-linking agent are melt kneaded in an extruder to perform dynamic cross-linking. However, said production process has problems such that (1) the process needs a step of kneading rubber and a thermoplastic resin prior to said dynamic cross-linking steps, and (2) the process is a complicated and inefficient one, because the process uses a batchwise kneading machine of low productivity such as a Banbury mixer and a kneader.
JP-A 58-25340 and JP-A 58-152023 disclose a process, wherein a mixture of an olefin copolymer rubber in a particle form with an olefin polymer resin in a pellet form is fed through a hopper to an extruder to perform melt kneading of said olefin copolymer rubber and said olefin polymer resin and then perform dynamic cross-linking. However, because the olefin copolymer rubber in a particle form is tacky, rubber having a size similar to that of a pellet can hardly be obtained; as a result, a size of the olefin copolymer rubber in a particle form becomes larger than that of the olefin polymer resin in a pellet form, so that the mixture thereof separates easily from each other in the hopper; and therefore, it is difficult to obtain a thermoplastic elastomer composition, which has a uniform composition ratio between the olefin copolymer rubber and the olefin polymer resin. Each of the references referred to above is incorporated herein by reference in its entirety.
While a thermoplastic elastomer composition is now spreading widely its uses as car interior parts such as an instrument panel (dashboard), which requires an excellent anti-fogging property, such a thermoplastic elastomer composition having an excellent anti-fogging property can hardly be obtained by the above-mentioned process, because a processing time required for a process for producing said composition is so long that the rubber and the resin are deteriorated during said processing to generate volatile low molecular weight compounds. Taking a car by way of example, various kinds of such volatile low molecular weight compounds contained in said composition evaporate, and then condense on a car windowpane to make the pane cloud, thereby causing an inconvenience of hindering the driver""s visibility. The above-mentioned term xe2x80x9canti-fogging propertyxe2x80x9d means the property free from said inconvenience.
Accordingly, it is an object of the present invention to provide a process for producing a thermoplastic elastomer composition with high efficiency, which has a uniform composition ratio.
It is another object of the present invention to provide a thermoplastic elastomer composition, which has an excellent anti-fogging property.
The present invention provides a process for producing a thermoplastic elastomer composition, which comprises the step of feeding rubber and a thermoplastic resin through feed throats independent of one another, respectively, to an extruder to perform melt kneading thereof, wherein the feed throats are connected to the extruder.
The present invention also provides a thermoplastic elastomer composition having a haze value of a glass plate of not higher than about 2%, provided that the haze value is measured with use of an apparatus according to regulations prescribed in ISO 6452 after a lapse of heating time of 20 hours at a heating temperature of 100xc2x0 C.
The present invention further provides a car interior part, (i) comprising the above-mentioned thermoplastic elastomer composition, and (ii) comprising the thermoplastic elastomer composition produced by the above-mentioned process.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.